Add allow-when-locked=true spawn bind property

wiki/Configuration:-Key-Bindings.md

@@ -113,6 +113,15 @@ binds {
 }
 ```
 
+Spawn bindings have a special `allow-when-locked=true` property that makes them work even while the session is locked:
+
+```
+binds {
+    // This mute bind will work even when the session is locked.
+    XF86AudioMute allow-when-locked=true { spawn "wpctl" "set-mute" "@DEFAULT_AUDIO_SINK@" "toggle"; }
+}
+```
+
 Currently, niri *does not* use a shell to run commands, which means that you need to manually separate arguments.
 
 ```